1. Field of the Invention
This invention relates to apparatus for drilling colinear (in the same line) holes in opposite directions through the walls of concentric pipes to form a single hole through the pipes. It is particularly applicable to large pipes such as casing used in wells.
2. Description of Related Art
After wells have produced to an economic limit it is necessary to remove pipes (casing) from the wells as part of abandoning the wells. There are normally several concentric casing strings to be removed. In offshore operations it may be desirable to reclaim a slot to drill a new well, eliminate a slot to reduce wave loading on a platform structure or to detach and remove a platform structure. When retrieving casing(s) it is normal practice to cold cut the casing(s) with an external saw into lengths that are within the safe lifting capacity of the available lifting apparatus.
Prior to removal of casing at the surface of a well, the well is plugged and all tubing and production casing that are free are removed from the well. An internal mechanical cutter may then be used to cut the remaining casings at a predetermined depth below the mud line. Once the down-hole internal cut has been completed it is desirable to form a hole through the diameter of the concentric pipes. Once the hole has been formed, a metal pin is inserted through the hole. During the cutting operation, the internal pipes may become displaced from the external pipe, causing inefficient cutting time and or damage to the saw. There is a need to stabilize the location of the concentric pipes.
The pin is left protruding out of the exterior pipe on each side of the concentric pipes. The first set of drilled holes is located at the upper end of the pipes, allowing sufficient metal above the holes for the metal pin to secure the inner pipes and to support the string weight of the pipes. The pin may then be used as a lifting device by attaching slings over the protruding ends of the pin and securing slings by sliding keeper plates with pin holes onto the pin against the slings and then installing keeper bolts through the pin diameter on each end. Once the slings are properly secured the pipes may then be safely lifted by means of winches, casing jacks, or a drilling rig to a selected length above the rig floor or work deck and then held in place by bowl and slips on the outermost casing. The process of forming holes simultaneously through the diameter of the pipes is then repeated a few feet above the bowl and slips and a second pin is installed through the pipes. Once the second pin has been installed, the pipes may then be cut with an external saw at a safe distance above the second pin to allow adequate casing material for the pin to secure the inner pipes and support the remaining string weight. Once the sawing operation is completed the first sectioned length of pipes may be removed and laid down Once the sectioned length of pipes has been laid down, the slings and the metal pin are removed. Wire cables may then be run through the drilled holes and secured with cable clamps to prevent internal pipes from sliding out during transportation. The securing cables are a safety precaution only and are not to be used as a lifting point. The process of securing the slings is then repeated onto the second pin, the slips are removed from the bowl, and the pipes may again be lifted to the determined length above the rig floor or work deck. The slips are then replaced into the bowl. The process of drilling, pinning, sawing, and laying down of sectioned pipes is repeated until the entire string of pipes has been removed.
The procedure described above is a typical method of recovering pipes from a platform well. However, there may be variations to the procedure based on platform structure and available work space. The forming of holes, pinning, and sawing process, for example, may be performed at the well bay level or other levels of the platform structure. Also, when bowl and slips are not available or practical for a given project, support beams may be used to hold the string weight. This method requires the same process as described above with the exception of an additional drill- and pin-step. Once the downhole internal cut has been completed the first set of holes may be formed and pinned at the upper end of pipes to secure slings and lift the pipes to a determined length above the rig floor and/or work deck. The second set of holes may then be formed and pinned just above the support beams. The pipe string load is then lowered until the pin material protruding through each side of the diameter of the pipes comes to rest on the support beam to hold the string weight. A third set of holes may then be formed and pinned just above the second pin to be used later as a pick up point. The pipes may then be cut with an external saw above the third pin. The length of sectioned pipes is then laid down, the pin removed and cables installed through the holes. The pipe removal process is continued by securing the slings onto the remaining upper pin, lifting the pipe to a level for safe removal of the lower pin previously resting on support beam, and then lifting pipe to the determined length above the rig floor and/or work deck. The procedure is repeated until the entire pipe string has been removed.
The hole through the concentric pipes may be formed by torch and by chipping cement between pipes. This procedure is slow and requires great care to remain safe. A drill may be used to drill a single hole through the concentric pipes, but this requires a long drill and consumes excessive time. What is needed is apparatus and method for forming colinear holes through concentric pipes and any material in the annuli between the pipes in a safe, efficient and cost-effective procedure. The apparatus should be adapted for use on concentric casings in wells that are located either on land or offshore at depths accessible to divers.